1. Field of the Invention
The present invention relates to a pattern correction required in lithography processing of semiconductor integrated circuits and liquid panels, and more particularly to a correction technology of a mask pattern for performing faithful pattern transfer to a design pattern.
2. Description of the Related Art
In a photolithography technology used in manufacturing processing of semiconductor integrated circuit and liquid crystal panels, an optical proximity effect has become more serious problem as an integrated degree more increases and design rules become more critical.
An optical proximity effect is phenomenon in which the design pattern is not transferred on a wafer in the intended shape and dimension. For example, such phenomenon that the dimension of a line pattern reduces in its long side direction or the corner portion of an L-shape line pattern is transferred in a round shape is the typical optical proximity effect. Although the optical proximity effect has originally meant an effect due to optical factors in pattern transfer, now it means an effect caused through the entire wafer processes.
When the optical proximity effect arises, deviation between the design pattern and a pattern actually formed occurs, and it is impossible to achieve desired device performance. Therefore, an optical proximity effect correction (OPC) is required to reproduce a pattern having the designed dimension and shape on a wafer. The optical proximity effect correction means changing selectively the shape of the pattern or the like on a mask in advance in consideration of a process conversion difference.
Various techniques have already proposed and carried out for the optical proximity effect correction. There are a simulation-based and a rule-based (alternatively referred to as a model based) methods as a method to prepare mask data by automatically executing the optical proximity effect correction (hereinafter referred to as “OPC” depending on the situation) on design data. The simulation-based OPC is a method in which an optical image in a mask pattern layout is calculated before a correction, a portion deviating from the pattern is detected, and the detected portion is corrected. This method shows high correction precision although much calculation amount is required, and is used for calculating a correction value for a line segment or an edge having importance among line segments and edges composing the pattern.
The rule-based OPC is a method to execute a correction such as mask bias according to rules. This method showing a high processing speed, determines the correction value according to predetermined rules, for each edge of a figure contained in a design layout to apply the correction value for an optical proximity effect correction.
In the conventional optical proximity effect correction, edges not meeting predetermined conditions, for example, edges having length shorter than predetermined values (hereinafter referred to as “minute edges”), are excluded from being subjected to the OPC. The OPC is executed only for edges having length longer than predetermined value. As a matter of course, the minute edges originally exist in the stage of design data, and they often occur as results of repeatedly performed complicated and minute pattern data processing prior to the OPC. If the minute edges exist, minute projections, minute hollows, acute projections and acute hollows are caused by the OPC itself and pattern data processing subsequent to the OPC. They are factors adversely affecting a mask drawing and a check.
FIGS. 1A and 1B illustrate the examples of occurrence of projections and hollows caused by the conventional optical proximity effect correction. In FIG. 1A, only edges 1002 and 1003 having length longer than predetermined values are objects of the OPC in a pattern 1001 shown by solid lines, which has not subjected to the OPC yet. The OPC to thicken the pattern was executed for the edges 1002 and 1003 while leaving a minute edge 1004 excluded from the object of the OPC at an initial position. As a result of the OPC, the corrected pattern 1005 illustrated by the dotted lines is obtained. In the pattern 1005 after the OPC, the minute hollow 1006 occurs.
In the case of FIG. 1B, in the pattern 1010 illustrated by the solid lines, which has not subjected to the OPC yet, the edges 1012 and 1013 meeting conditions are similarly objects of the OPC, and the minute edges 1014 and 1015 are excluded from the object of the OPC. As a result, the pattern 1020 illustrated by the dotted lines is obtained. In this case, an acute projection and a slanting slit occur as illustrated by the circle A.
These minute projections (acute pattern) and these minute hollows increase a data amount uselessly, and decrease mask drawing precision. In addition, a mask drawing time becomes much longer. In checking mask defects process, they are apt to be detected as suspected failure, and much time and labor are needed for error detection.
In order to erase minute unevenness caused by the OPC, a method has been known, in which a slightly thick/thin bias or a slightly thin/thick bias is applied to the whole of a layout after the OPC, and minute projections and minute hollows are erased. However, projections and hollows may be caused additionally at unexpected spots by performing such bias processing. Also disadvantageous deformation such as a short and slit may occur. Moreover, there are many shapes having projections and hollows that are not erased only by the bias processing.
For example, as shown in FIG. 2A, the pattern 1030 obtained by the OPC processing has the minute hollow 1031 and the minute projection 1032. When slightly thick bias is first applied to the pattern 1030, the hollow 1031 is made to be flat, and the pattern 1035 illustrated in FIG. 2B is obtained. When slightly thin bias is further applied to the pattern 1035, the pattern 1037 having dimensions which are almost equal to those of the initial pattern is obtained as shown in FIG. 2C. In this situation, although the hollow 1031 is erased, the extremely acute hollow 1033 occurs.
When slightly thin bias is further applied to the pattern 1037, the pattern 1039 in which the projection 1032 is erased is obtained as shown in FIG. 2D. Then, by applying slightly thick bias to the pattern 1039, the pattern 1041 in which the hollow 1031 and the projection 1032 are finally erased is obtained as shown in FIG. 2E.
However, the acute hollow 1033 illustrated by the circle B is not erased in spite the bias processing is executed over and over again. The acute hollow on the mask pattern is undesirable because this acute hollow is a cause of suspected error detection in checking the mask process as well as a cause of a decrease in mask drawing precision.
On the other hand, when the correction values for the respective minute edges, which are left at initial positions in the pattern, and unevenness are individually calculated by the simulation-based method after the OPC processing, the calculation amount and the processing time are enormous, and such individual calculations are impractical